U.S. Pat. No. 4,126,605 (Schneider) described a process for obtaining a product suitable for intravenous administration from Cohn Fraction II gamma globulin. Cohn Fraction II is dissolved in a buffered aqueous solution at pH 6.7. The solution contains hydroxyethyl starch. After filtering the solution, polyethylene glycol is added to a concentration of 10%. After removal of the precipitate, additional polyethylene glycol is added to the solution to a concentration of 20%. The precipitate which results is improved unmodified gamma globulin suitable for intravenous use.
U.S. Pat. No. 4,165,370 (Coval) describes a process for obtaining a product suitable for intravenous administration from Cohn fraction II gamma globulin. Cohn fraction II is dissolved in solution having an acid pH of 4.8 to 6.5 and a low ionic strength, i.e., having a conductance of about 300-10.sup.-6 cm.sup.-1 ohm.sup.-1. After filtering the solution, polyethylene glycol, molecular weight 4,000, is added first to a 4% concentrate, then 5% concentrate. After the solution is centrifuged and any precipitate is removed, additional polyethylene glycol is added to the solution to a 12% concentration. The resulting precipitate is an immunologically active unmodiifed gamma globulin suitable for intravenous use.
In the above mentioned processes, the yields of pure gamma globulin are about 30% of the gamma globulin of the Cohn Fraction II. Modifications have been made to increase yields, but the increased yield has generally been at the expense of purity. An increased yield at constant quality of the product has not yet been possible.
It is an object of the present invention to isolate gamma globulin of high purity, suitable for intravenous use, in high yield.